<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
</head>
<body>
<div id="app">
  <input name="tmp" type="radio" value="-1" v-model="tmpAge_c"> <br>
  <input name="tmp" type="radio" value="-2" v-model="tmpAge_c">
  <select v-model="age" @change="setAge">
    <option v-bind:value="item -2" v-for="item in 10">{{item - 2}}</option>
  </select>
</div>
</body>
</html>
<script src="../node_modules/vue/dist/vue.js"></script>
<script>
  var options = {
    data: function () {
      return {
        age: -1,
        tmpAge: -1
      }
    },
    computed: {
      tmpAge_c: {
        get: function () {
          return this.tmpAge
        },
        set: function (val) {
          if (val === '-1') {
            this.tmpAge = -1
            this.age = -1
          }
        }
      }
    },
    methods: {
      setAge: function () {
        this.tmpAge = -2
      }
    }
  }
  var vm = new Vue(options)
  vm.$mount('#app')
</script>
